Prediction of asphaltene precipitation during CO2 injection

Aimed at the possible phenomenon of asphaltene precipitation during CO2 injection, the equation of state established by Anderko was introduced to describe the phase behavior of precipitated asphaltene because of its strong polarity. The fugacity of the precipitated asphaltene component was derived and a calculation model of gas-liquid-asphaltene equilibrium was constructed. After matching of PVT experimental data from a reservoir, the model was used to calculate the volume of precipitated asphaltene during CO2 injection. The precipitation model suggests that for a constant injection pressure, the asphaltene precipitation first increases and then decreases as CO2 increases with the asphaltene precipitation reaching a maximum when the gas phase occurs in the system. When the CO2 mole percentage of the CO2-oil system is constant, the precipitated asphaltene reaches a maximum at the saturation pressure.